The sample size was calculated based on the national prevalence of 19.2% of FTPI in dairy calves (13 (link)), compared to a historical FTPI prevalence of 8–10% on the two farms, a type 1 error of 5%, power of 80%, and a 2-sided test using the exact Agresti-Coull method. The minimal sample size required was 132 calves. To account for a 10% drop-out due to missing values or samples, at least 145 calves were enrolled. A statistical software was used for sample size calculation (JMP Pro v16.2.0, SAS Institute, Cary, NC).
Calves were separated from cows after parturition and identified using radiofrequency ear tags and weighed using an electronic scale (WW-Paul Scales Model IQ+710, Duncan, OK). Calves were then housed in individual calf hutches. The volume of pooled colostrum fed to calves was based on the time of the day when the calves were born. Calves born between 5 am and 5 pm were fed 4 L of colostrum once by oroesophageal tubing. Calves born between 5 pm and 5 am were fed 2 L of colostrum immediately by oroesophageal tubing, then another 2 L by oroesophageal tubing at 5 am on the next day. This colostrum feeding protocol was part of the farms' standard operating procedures based on the availability of labor, and we had no influence on the protocol. After 24 h of age, calves were fed 2 L of heat-treated milk with added milk replacer three times daily, a commercial starter feed, and water, ad libitum. Blood was collected at 24–72 h of age, and serum was harvested after centrifugation at 2,800 × g. Morbidity and mortality events were recorded using an electronic record system. Calves were weaned at 10 weeks of age.
Calves were separated from cows after parturition and identified using radiofrequency ear tags and weighed using an electronic scale (WW-Paul Scales Model IQ+710, Duncan, OK). Calves were then housed in individual calf hutches. The volume of pooled colostrum fed to calves was based on the time of the day when the calves were born. Calves born between 5 am and 5 pm were fed 4 L of colostrum once by oroesophageal tubing. Calves born between 5 pm and 5 am were fed 2 L of colostrum immediately by oroesophageal tubing, then another 2 L by oroesophageal tubing at 5 am on the next day. This colostrum feeding protocol was part of the farms' standard operating procedures based on the availability of labor, and we had no influence on the protocol. After 24 h of age, calves were fed 2 L of heat-treated milk with added milk replacer three times daily, a commercial starter feed, and water, ad libitum. Blood was collected at 24–72 h of age, and serum was harvested after centrifugation at 2,800 × g. Morbidity and mortality events were recorded using an electronic record system. Calves were weaned at 10 weeks of age.
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